Applications in the millimeter-wave frequency regime have gained significant interest in the past few years due to the rapid advancement in low cost semiconductor technologies such as silicon germanium (SiGe) and fine geometry complementary metal-oxide semiconductor (CMOS) processes. Availability of high speed bipolar and metal-oxide semiconductor (MOS) transistors has led to a growing demand for integrated circuits for mm-wave applications at 60 GHz, 77 GHz, and 80 GHz and also beyond 100 GHz. Such applications include, for example, automotive radar and multi-gigabit communication systems.
In some radar systems, the distance between the radar and a target is determined by transmitting a frequency modulated signal, receiving a reflection of the frequency modulated signal, and determining a distance based on a time delay and/or frequency difference between the transmission and reception of the frequency modulated signal. Resolution, accuracy and sensitivity of the radar system may depend, in part, on the phase noise performance and frequency agility of the radar's frequency generation circuitry, which generally includes an RF oscillator and circuitry that controls the frequency of the RF oscillator. One of the factors that affects phase noise performance is the amplitude of the oscillation signal produced by the RF oscillator. However, in many RF oscillators, the saturation of active devices used to generate the oscillations may limit the amplitude of the oscillation signal.